What happened
On 15 September 2012, a Beech B200 Super King Air, registration G-SYGA, was conducting a non-revenue medical flight from Wick to Glasgow. During the approach to Glasgow Airport, the co-pilot, acting as the handling pilot, reduced engine power to manage the descent speed. This power reduction triggered the landing gear warning horn.
While attempting to silence the horn, the co-ability mistakenly pressed the go-around button instead of the warning horn silence button. This action caused the autopilot to disengage and all flight director modes to drop out. The sudden change in cockpit indications distracted the crew, leading to a breakdown in situational awareness. Consequently, the aircraft descended through its cleared altitude of 3,500 ft, reaching a minimum altitude of 2,273 ft. The Air Traffic Controller observed the deviation and alerted the crew, who then manually recovered the aircraft to the required altitude.
The investigation
The AAIB investigation focused on the differences between the cockpit of G-SYGA and the more modern Pro Line 21 electronic flight information systems (EFIS) that the crew was accustomed to. Unlike the EFIS version, this aircraft utilized conventional mechanical flight instruments. The investigation found that the co-pilot had recently completed training on EFIS-equipped aircraft and had received only an informal briefing regarding the mechanical instrument layout of this specific B200.
Investigators noted that the physical location of the buttons—specifically the go-around button and the warning horn silence button—differed significantly from the Pro Line 21 standard. The co-pilot's attempt to locate the silence button on the power lever resulted in the accidental activation of the go-around mode.
Findings
- The crew experienced a loss of situational awareness due to the distraction of the gear warning horn and the subsequent autopilot disengagement.
- The co-pilot was unfamiliar with the specific cockpit layout of the G-SYGA, which lacked the electronic displays and centralized annunciators found in Pro Line 21 aircraft.
- The lack of formal differences training for converting from EFIS to mechanical instruments was a primary contributing factor.
- The co-pilot had received only an informal ground briefing rather than a structured training programme regarding the mechanical instrumentation differences.